Method for making a gas blocking cable

ABSTRACT

A gas blocking cable includes cabled wires, where each wire includes cabled conductors having interstitial areas there between. An insulation material circumferentially surrounds the cabled conductors and a conductor filling material is positioned within the interstitial areas between conductors. A shield circumferentially surrounds the cabled wires so that a cable is formed with areas between the wires. A wire filling material is positioned within the areas between the wires. Each of the conductor filling material and wire filling material is inert, non-flammable and able to withstand a temperature of at least approximately 200° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation to U.S. Non-Provisional patentapplication Ser. No. 13/650,729 filed Oct. 12, 2012, now U.S. Pat. No.9,837,187, entitled GAS BLOCKING CABLE AND METHOD OF MANUFACTURING,which claims priority to U.S. Provisional Patent Application Ser. No.61/547,168, filed Oct. 14, 2011, the disclosures of each of which areincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to multi-conductor cables and,more particularly, to a multi-conductor cable capable of blockingpassage of high pressure gases and other fluids through the interstitialspaces of the cable and a method of making the cable.

BACKGROUND

Power generation turbines are typically housed in containment areas toprotect individuals in the event of an explosion. Sensors from theturbines communicate with instrumentation and equipment in the turbinecontrol room via multi-conductor sensor cables. In the event of anexplosion in the turbine containment area, when conventionalmulti-conductor cables with no gas blocking capabilities are used, highpressure, hazardous gases will travel through the interstitial spaces ofthe cables and will reach control rooms and may cause harm to peopleoperating the control room. Historically, gas blocking is achieved onlyin a cable gland assembly connection to the frame wall. Such anapproach, however, leaves a leak path through the interstitial space inthe cable. A need exists for a multi-conductor cable that eliminatesinterstitial leak paths.

The marine industry has been using water blocked cables for many years.Such cables, however, would fail to prevent the leakage of hazardoushigh pressure gases in the event of an explosion. Furthermore, suchcables cannot withstand the high cable operating temperature environmentof a power generation turbine application (up to 200° C.).

The IEC (International Electro-technical Commission) releasedSpecification EN-60079-14 in 2008. This specification coversinstrumentation cables that are used on power generation turbines. Aneed therefore exists for cables that meet the new stringent IECrequirements. Although fluid blocking technology is used in water blockcables, as noted previously, the temperature rating and pressurerequirements of the “explosion proof” cables necessary to meet the IECrequirements are far beyond the capability of the technology in waterblock cables.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an embodiment of the gas blockingcable of the invention;

FIG. 2 is a schematic view of a first embodiment of an applicationdevice for use in creating the cable of FIG. 1;

FIG. 3 is a schematic cross sectional view of the applicator of theapplication device of FIG. 2;

FIG. 4 is a schematic cross sectional view of a second embodiment of anapplication device for creating the cable of FIG. 1;

FIG. 5 is a schematic cross sectional view of a third embodiment of anapplication device for creating the cable of FIG. 1;

FIG. 6 is a schematic cross sectional view of a fourth embodiment of anapplication device for creating the cable of FIG. 1;

FIG. 7 is a flow chart illustrating an embodiment of the gas blockingcable making process of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

While the gas blocking cable of the invention is described below interms of a power generation turbine application, it may be used forother applications by varying the chosen materials and configuration(number of conductors, wires, etc.). Due to the many variations of themulti-conductor cables used in these applications and the non-circularcross-section of these cables, a configuration that is not too deviantfrom existing cables is preferable. This enables the end user to use thecables of the invention without significant changes to the hardware andinstallation process. This introduces the challenge of filling thelarger interstitial spacing between the conductors requiring fillingcompounds that can be cured after the processing and that will notaffect the flexibility of the cables.

Gas fluid leakage can occur through a) the spaces between the strands ofthe conductors, b) the space between the individual wires made up ofinsulated stranded conductors, and c) the space between Aluminum/Mylartape and outer Fluoro-polymer jacket. Thus, it is clear that these threepaths need to be blocked to meet the requirements of a gas blockingcable.

An embodiment of the gas blocking cable of the present invention isindicated in general at 10 in FIG. 1. The illustrated embodimentincludes a number of insulated conductors 12. As an example only, theconductors may be 14 AWG, 19 strand, silver plated copper wire. Thestrand interstitial spaces or areas 15 are filled with a siliconecompound. An insulation material 18 circumferentially surrounds theconductors. Insulation 18 may be, as an example only, helically wrappedpolyimide tape with an overcoat of liquid polyimide that is heat cured.

The wires 20 a and 20 b, which are made up of the insulated conductors12, are twisted with a drain wire 22 and a filler 24 to provide thecable with a round profile. The drain wire 22 is, as an example only, a16 AWG tin plated copper wire. The high temperature filler 24 ispreferably extruded silicone or FEP monofilament.

The twisted wires 20 a and 20 b, drain wire 22 and high temperaturefiller member 24 are wrapped with a shield 36 so that they arecircumferentially surrounded. The shield 36 may be, as an example only,Aluminum/Mylar tape. The spaces or areas 38 between the twisted wires,drain wire and high temperature filler are filled with a siliconecompound.

A jacket 42 is extruded over the shield 36 and may be, as an exampleonly, extruded FEP (Fluorinated Ethylene Propylene). As an example only,the nominal diameter of the jacket layer 42 may be 0.212 inches. A hightemperature fiberglass braid 44 preferably covers the jacket 42 while astainless steel braid 46 preferably covers the fiberglass braid 44. Insome cable configurations, an additional extruded FEP jacket is appliedover the stainless steel braid.

It is to be understood that the embodiment of the gas blocking cable ofFIG. 1 is an example only, and that the cable of the invention could beconstructed with many alternative materials and number of any of theconductors, wires, drain wires and/or fillers in many alternativeconfigurations.

A variety of filling material compounds may be used to fill theinterstitial and other spaces or areas in the cable in the mannerdescribed above. The filling material must be inert, non-flammable andable to withstand, and suitable for operation, temperatures up to atleast approximately 200° C. A two-part, room temperature curablesilicone compound preferably is used. While such a silicone compound ispreferably used, other suitable compounds in the art may alternativelybe used. Examples of suitable silicone compounds include, but are notlimited to, the following:

-   -   a. One-part heat cure silicone, TSE-322 made by Momentive.    -   b. CST-2127, two-part silicone. This is a room-temperature cure        two-part silicone compound available from Cri-Sil Silicone        Technologies LLC of Biddeford, Me.    -   c. CST-2327, two-part silicone. This is a modified version of        CST 2127 and is the preferred silicone compound for use, for        example, in the embodiment of FIG. 1, and is also available from        Cri-Sil Silicone Technologies LLC of Biddeford, Me.

In order to get the compound into the space between the differentinsulated conductors and wires, it has to be applied during the cablingprocess or in a separate process right before the Aluminum/Mylar tapesgoes on the cable. Embodiments of application devices that may be usedfor this purpose are illustrated in FIGS. 2-6. The filling material maybe applied before or after conductors and/or wires are twisted. Multipleapplication devices may be used in series as required to produce thecable based on the configuration and intended use of the cable.

The following examples assume that, with reference to FIG. 1, the wires20 a and 20 b have been provided by a supplier with their interstitialspaces 15 filled with a silicon compound (such as those described above)or another suitable material.

A first embodiment of the application device is indicated in general at47 in FIG. 2. As illustrated in FIGS. 2 and 3, the application devicefeatures and applicator, illustrated at 48 in FIGS. 2 and 3. Asillustrated in FIG. 3, the applicator includes an application housing 50that encloses a pressure chamber 52, through which the twisted wires(and any filler such as 24 of FIG. 1) 54 travel during the cablingoperation just prior to the taping operation.

With reference to FIG. 2, one part (55 a) of a two-part siliconecompound is pumped from a drum 56 a using a plunger system or hydraulicpump 58 a, while the other part (55 b) of the two-part silicone compoundis pumped from drum 56 b using plunger system or hydraulic pump 58 b.Other pumping devices known in the art may be used in place of plungersystem or hydraulic pumps 58 a and 58 b. The pressurized flows of thefirst and second parts of the silicon compound from drums 56 a and 56 bare mixed in a mixing nozzle 60 and then flow to the applicator 48 vialine 62. With reference to FIG. 2, the flow of the pressurized, mixedsilicon compound 64 through line 62 pressurizes the chamber 52 withsilicone compound as the wires (and any filler) 54 pass through thechamber. As an example only, the preferred pressure of chamber 52 isapproximately 2000-5000 psi.

A second embodiment of the application device is indicated in general at72 in FIG. 4. In this embodiment, a silicone compound (such as a mixedtwo-part silicone compound) 74 is stored within a chamber 76. Apressurizing device 78 causes the chamber 76 to be pressurized. Thetwisted wires (and filler) 80 travel through orifices or dies 77 a and77 b (which serves as a sizing die) of the chamber 76 so that thesilicone compound is applied thereto. A supply line 82 leading from asupply of the silicone compound replenishes the silicone compound 74.Examples of suitable pressurizing devices 78 include an air pump, apiston device (where the piston acts on the silicone compound 74) or, insimpler cable configurations, merely passing the cable through anunpressurized container filled with silicone is sufficient to giveadequate deposits of silicone to the cable.

A third embodiment of the application device is indicated in general at92 in FIG. 5. In this embodiment, a silicone compound (such as a mixedtwo-part silicone compound) 94 is stored in a container 96 and thetwisted wire (and any filler) 98 is “passed through” this containerusing groove or pulley device 102 as shown so that the silicone compoundis applied thereto.

A fourth embodiment of the application device is indicated in general at104 in FIG. 6. In this embodiment, a silicone compound (such as a mixedtwo-part silicone compound) 106 is stored in a container 108 and thetwisted wire (and any filler) 110 is “passed through” orifices or dies112 a and 112 b (which serves as a sizing die) in the container so thatthe silicone compound is applied thereto.

As noted previously, the application device fills the cable with thesilicone compound at the cabling stage prior to the taping stage. In thecase of the embodiments of FIGS. 3, 4 and 6 sizing die 66 (FIG. 3), 77 b(FIG. 4) or 112 b (FIG. 6) on the chamber outlets smoothes the surfaceof the cable as it exits the application devices. The tape then goesover the silicone compound, wires and filler using processes known inthe prior art (such as, as an example only, U.S. Pat. No. 4,767,182 toParfree et al., the contents of which are hereby incorporated byreference) and further encapsulates the silicone compound, wires andfiller. While the silicone compound is still in a “mushy” stage, thetape provides containment. The process must be robust enough to fill allthe space between the conductors.

The next process is extrusion of the FEP (Fluorinated EthylenePropylene) jacket over the Aluminum/Mylar tape. Since the Mylar side ofthe tape and plastic on the jacket doesn't fuse, the space between thetape and the jacket is another potential leak path. A layer of thesilicone compound (such as those described above), indicated at 114 inFIG. 1, is applied over the Aluminum/Mylar tape, using a secondapplication device. This application device may be of the type shown inany of FIGS. 2-6, or any other application device known in the art, toclose this leak path. Preferably, a surplus amount of silicone compoundis applied in one application so that there is a remnant layer ofsilicone on the Aluminum/Mylar tape.

The entire cable is then post cured (with or without the application oftemperature) to set the silicone compound. The curing can be achieved,for example, a) in 24 hours either by room temperature vulcanization ofthe compound, or b) in 3-4 hours by placing the cables in an aircirculating oven for 4-6 hours at 150° F.

Braids (such as 44 and 46 of FIG. 1) may then be applied to the cableusing processes well known in the art.

As noted previously, the supplier of the wire preferably applies thecorrect amount of silicone compound or other filling material betweenthe conductor strands, sufficient to seal the leakage path between theconductor strands. Alternatively, an application device of the typeshown in FIGS. 2-6, or any other application device known in the art,may be used to close the leak paths between the conductors of the wire.

An illustration of a process for making a gas blocking cable in anembodiment of the invention is illustrated in FIG. 7 where 120illustrates cabling insulated conductors (such as 12 in FIG. 1). Afterthe insulated conductors are cabled, or while they are being cabled,filling material, such as silicone compound, is applied to theinterstitial space (15 in FIG. 1) using one or more of the applicationdevices of FIGS. 2-6 as indicated at 122. As indicated at 124, aninsulation material (18 in FIG. 1) such as a polyimide tape with anovercoat of liquid polyimide is then applied to form a wire (20 a and 20b of FIG. 1). As indicated at 126, the wire (20 a, 20 b and 22 ofFIG. 1) and any filler (24 of FIG. 1) are cabled next. Filling material,such as silicone compound is then applied at 128 to the spaces (38)between the twisted wires and filler using one or more of theapplication devices of FIGS. 2-6. A shield (36 in FIG. 1) such asAluminum Mylar tape, is then applied at 130. As indicated at 132, theshield is coated with a layer of filling material such as siliconecompound. Next, at 134, extrusion of the FEP (Fluorinated EthylenePropylene) jacket (42 in FIG. 1) over the shield occurs. Finally, asshown at 136, braids (44 and 46 in FIG. 1) are applied to the cable.

The multi-conductor cable described above is capable of blocking passageof gas/fluid through the interstitial spaces in the multi-conductorcable to prevent passage of high pressure gases in turbine and powergeneration applications.

The cable described and constructed in the manner above is able to passa fluid (oil) leakage test at a high pressure of 435 psi (about 3000kPa) and may withstand temperatures up to approximately 200° C. andstill maintains flexibility.

While the preferred embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications may be made therein without departing from the spiritof the invention, the scope of which is defined by the appended claims.

We claim:
 1. A method for making a gas blocking cable comprising thesteps of: a) cabling a plurality of conductors so that a first set ofinterstitial areas are formed there between; b) applying a conductorfilling material to the first set of interstitial areas between theplurality of conductors so that the first set of interstitial areas arefilled, where the conductor filling material is inert, non-flammable andable to withstand a temperature up to at least approximately 200° C.; c)applying an insulation material so as to circumferentially surround theplurality of conductors and conductor filling material so that a firstwire is formed; d) repeating steps a) through c) so that a second wireis formed; e) cabling the first and second wires so that a second set ofinterstitial areas are formed there between; f) pumping a first part ofa wire filling material and a second part of a wire filling material; g)mixing the first part of the wire filling material and the second partof the wire filling material together in a mixing nozzle, therebycreating the wire filling material; h) applying, with an applicationdevice, the wire filling material to the second set of interstitialareas between the first and second wires so that the second set ofinterstitial areas are filled by passing the first and second wiresthrough a pressure chamber with the wire filling material to apply thewire filling material to the first and second wires, where the wirefilling material is inert, non-flammable and able to withstand atemperature up to at least approximately 200° C.; i) applying a shieldmaterial so as to circumferentially surround the first and second wiresand the wire filling material; j) applying a jacket material over theapplied shield material, wherein the jacket material is extruded andcircumferentially surrounds the shield material with a jacket fillingmaterial positioned within a third set of interstitial areas between theshield material and the jacket material, where the jacket fillingmaterial is inert, non-flammable and able to withstand a temperature upto at least approximately 200° C.; and k) braiding a fiberglass materialover the applied jacket material, wherein the gas blocking cable blocksa passage of a high pressure gas or a high pressure fluid through thefirst set of interstitial areas, the second set of interstitial areas,and the third set of interstitial areas to prevent the passage of thehigh pressure gas or the high pressure fluid.
 2. The method of claim 1further comprising the steps of curing the applied conductor fillingmaterial and curing the applied wire filling material.
 3. The method ofclaim 1, wherein the first wire and the second wire are twisted.
 4. Themethod of claim 3, wherein a drain wire is twisted along with the firstwire and the second wire.
 5. The method of claim 1, wherein the highpressure gas or the high pressure fluid is up to 435 psi (or about 3,000kPa).
 6. The method of claim 1, wherein the gas blocking cable passes afluid leakage test at a high pressure test of 435 psi (or about 3,000kPa) and can withstand temperatures up to approximately 200° C.
 7. Themethod of claim 1, wherein the wire filling material and the conductorfilling material are different materials.
 8. The method of claim 1,wherein the wire filling material is a silicone compound.
 9. The methodof claim 1, wherein the conductor filling material is a siliconecompound.
 10. The method of claim 1, wherein the jacket filling materialis a layer of a silicone compound applied over the shield material.